There are many industrial and commercial applications wherein two or more fluids must be brought into contact with each other. For example, it may be desirable to absorb soluble pollutants such as SO.sub.2, HCl etc. from air with water, which may or may not contain chemicals to remove the pollutants from the air supply. When removing soluble pollutants in this manner, the size and efficiency of the liquid-fluid contacting device is an important consideration in the design of such equipment.
There are a number of liquid-fluid contacting devices presently available. Spray dryers and scrubbers are widely used in chemical industries for drying and for pollution control applications. In these devices, liquid is dispensed by an atomizer as tiny droplets within a gaseous stream. To distribute liquid droplets over a wide cross-sectional area, a large liquid distribution piping network and a large number of atomizers are required. Moreover, a relatively large amount of energy is required to atomize the liquid. Further drawbacks with these systems include low transfer rates between soluble particles in the gas and liquid solvents and the possible lack of full contact between the gas and liquid as spraying is not uniform over the entire cross-section of an interaction chamber. The cost of such systems may be exceedingly high and efficiency low for many applications.
Packed columns contain solid internals such as Rashing rings, Berle saddles, Pall rings, stacked metallic sieves etc. wherein liquid falling over the packings is dispersed thereover to wet the surface thereof. The packings are designed to create a large liquid-dispersed surface area. Despite the many varieties of packings however, it is still difficult to provide an even distribution of liquid thereover. In addition, packed columns are not suitable for cleaning gas with high dust loadings as the dust accumulates within the packings. Moreover, high power consumption, channelling, flooding and loading are other operational drawbacks associated with packed columns.
Tray columns are widely used in industries, refineries and chemical plants. Tower internals are expensive. Use of downcomers within the tower for liquid flow from one tray to the other reduces gas flow area and increases tower diameter. Liquid gradient in the tray give rise to inefficient gas-liquid contacts. High pressure drop in the gas phase is another substantial drawback.
Wetted wall columns are characterized by small surface contact area compared to the overall volume of the equipment. Such columns are not suitable for large scale operations.
A number of devices employing threads, filaments etc. for distributing liquid for efficient liquid-fluid contact are known. U.S. Pat. No. 3,748,828 issued Jul. 31, 1973 to Akzo Belge S.A. discloses a process and apparatus wherein liquid is delivered to the end of a series of multi-filament threads arranged in at least one bundle so that liquid flows over each individual thread as a sheath therearound. A second fluid flows over the liquid sheaths to transfer heat or particles between the two fluids. This reference teaches that adjacent threads be sufficiently separated apart so that the individuality of every liquid sheath flowing along each thread is substantially retained.
U.S. Pat. No. 1,755,011, issued Apr. 15, 1930 to W. V. Ludlam discloses an air cleaner or filter device in which oil is fed into an upper chamber. The oil is allowed to seep down to a lower chamber containing a plurality of apparently randomly spaced vertical filaments consisting of hair or bristles, which are arranged around a central open passageway.
In U.S. Pat. No. 3,766,717 issued Oct. 23, 1973 to V. W. Belt, water is sprayed in the form of droplets to an incoming air flow. Numerous tubes are secured in a plate so that the tube bottom ends are just above the static water level below. The sprayed water accumulates over the plate and runs through both the inside and outside of the tubes like wetted wall columns.
In each of the above noted patent references, there is only limited surface contact between liquid and gas. Means for more intimate and repeated contact are desired for greater heat and/or material transfer efficiency.